1. The Muscular System: Part B10
The Muscular System: Part B

2. Muscles of the Thorax Muscles of respiration
External intercostals—more superficial muscles that elevate ribs for inspiration
Internal intercostals—deeper muscles that aid forced expiration
Diaphragm
Partition between thoracic and abdominal cavities
Most important muscle in inspiration
Innervated by phrenic nerves

3. External
intercostal
(a)
Internal
intercostal
Figure 10.10a

4. Xiphoid process of sternum Foramen for inferior vena cava Foramen for
esophagus
Costal cartilage
Central
tendon of
diaphragm
Diaphragm
Foramen
for aorta
Lumbar
vertebra
12th rib
Quadratus
lumborum
(b)
Psoas major
Figure 10.10b

5. Muscles of the Abdominal Wall
Four paired muscles; their fasciae and aponeuroses form the lateral and anterior abdominal wall
Internal obliques
External obliques
Transversus abdominis
Rectus abdominis

6. Transversus abdominis
Pectoralis major
Serratus anterior
Linea alba
Tendinous
intersection
Transversus abdominis
Internal oblique
Rectus
abdominis
External oblique
Aponeurosis of the
external oblique
Inguinal ligament
(formed by free
inferior border of
the external oblique
aponeurosis)
(a)
Figure 10.11a

7. Muscles of the Abdominal Wall
Fascicles of these muscles run at angles to one another, providing added strength
All are innervated by intercostal nerves
Actions of these muscles
Lateral flexion and rotation of the trunk
Help promote urination, defecation, childbirth, vomiting, coughing, and screaming

8. Rectus abdominis Internal External oblique oblique Lumbar fascia
IIiac crest
Pubic
tubercle
Lumbar
fascia
Transversus
abdominis
Inguinal
ligament
(b)
Figure 10.11b

9. Muscles of the Pelvic Floor
Pelvic floor (pelvic diaphragm) is composed of two paired muscles
Levator ani
Coccygeus
Both are innervated by sacral nerves

10. Muscles of the Pelvic Floor
Functions of the pelvic diaphragm
Seals the inferior outlet of the pelvis
Supports pelvic organs
Lifts pelvic floor to help release feces
Resists increased intra-abdominal pressure

11. Muscles of the Perineum
Urogenital diaphragm
Anterior half of perineum, inferior to pelvic floor
Deep transverse perineal muscle
External urethral sphincter (voluntary control of urination)

12. Anterior Pubococcygeus Symphysis pubis Levator ani IIiococcygeus
Urogenital diaphragm
Urethra
Vagina
Anal canal
Obturator
internus
Coccyx
Levator ani
Piriformis
Coccygeus
Pelvic
diaphragm
Posterior
(a)
Figure 10.12a

13. Urethral opening External urethral sphincter Vaginal opening
Inferior pubic ramus
Deep
transverse
perineal
muscle
Central tendon
Anus
External anal
sphincter
Male
Female
(b)
Figure 10.12b

14. Muscles of the Perineum
Muscles of superficial perineal space
Ischiocavernosus
Bulbospongiosus
Superficial transverse perineal muscles
External anal sphincter (in posterior half of perineum)

15. Urethral opening Clitoris Vaginal Anus opening Penis Midline raphe
Ischiocavernosus
Bulbospongiosus
Superficial
transverse
perineal muscle
Levator ani
Gluteus maximus
Male
Female
(c)
Figure 10.12c

16. Superficial Muscles of the Thorax
Most are extrinsic shoulder muscles
Act in combination to fix the shoulder girdle (mostly the scapula) and move it to increase range of arm movements
Actions include elevation, depression, rotation, lateral and medial movements, protraction, and retraction
Two groups of muscles: anterior and posterior

17. Superficial Muscles of the Thorax
Anterior extrinsic shoulder muscles
Pectoralis minor
Serratus anterior
Subclavius
(Pectoralis major considered later with muscles that act on the humerus)

18. Sternocleido- mastoid Subclavius Clavicle Subscapularis Deltoid
Pectoralis minor
Pectoralis
major
Coracobrachialis
Sternum
Serratus anterior
Biceps brachii
Humerus
(a)
Figure 10.13a

19. Superficial Muscles of the Posterior Thorax
Posterior extrinsic shoulder muscles
Trapezius
Levator scapulae
Rhomboids (major and minor)
(Latissimus dorsi considered later with muscles that act on the humerus)

20. Levator scapulae Trapezius Supraspinatus Clavicle Deltoid Spine of
Rhomboid
minor
Infraspinatus
Rhomboid
major
Teres minor
Teres major
Humerus
Latissimus
dorsi
(c)
Figure 10.13c